Trading resumed on the New York Stock Exchange floor around 3:10 p.m. ET Wednesday after a technical issue caused a more than three and a half hour halt.
Trading stopped around 11:30 a.m. ET due to what the exchange called an "internal technical issue." The NYSE said it did not suspect a cyberattack.
"I can't say with precision exactly what drove it," NYSE President Thomas Farley told CNBC. "We found what was wrong and we fixed what was wrong and we have no evidence whatsoever to suspect that it was external."
"There is no indication that there are malicious actors involved," White House Press Secretary Josh Earnest said, adding that the White House is monitoring the situation.
The issues did not affect the electronic NYSE Arca and NYSE Amex/Arca Options. The Nasdaq reported no technical problems, saying it continued to trade NYSE-listed stocks during the halt.
By about 3:15 p.m. ET, the NYSE said "all systems are functioning normally" except the Openbook data feed for the NYSE MKT primary markets. Volume was light after floor trading restarted and closing auctions continued as normal.
The NYSE said all open orders before the halt, including market on close, limit on close and closing offset, were canceled.
"Do we need to change our protocols? Absolutely. This can't happen again. We can't put ourselves in this position again. Exactly what those changes are, I'm not yet prepared to say," Farley said.